Fixed an outdated image, incorrect documentation for the Water resource game, and some typos.

doc/figs/configuration/configuration-game-admin-smartgrid-designer-new-level.png
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* Replaced old image with current one that shows the "Unlock condition" field.

doc/challenge-design-game-admin-smartgrid-game.rst
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* Fixed some typos.

doc/challenge-design-game-admin-resource-game.rst
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* Fixed "From Energy Goal Games to Resource Goal Games" to note that the water resource game is **enabled** by default, not disabled
* Fixed some typos.